STRESS FRACTURES IN THE TRANSFER CASE ALUMINUM INTERCOOLER LOOP OF THE AUTOMATIC TRANSMISSION COOLING CIRCUIT CAUSED DESTRUCTION OF THE TRANSMISSION DUE TO LACK OF TRANSMISSION OIL. THIS SAME DEFECT HAS BEEN NOTED IN AT LEAST THREE AM GENERAL HUMMERS, AND A SUDDEN LOSS OF ATF FLUID MAY RESULT IN A CATASTROPHIC FAILURE OF THE TRANSMISSION AT SPEED, POSSIBLY CAUSING A CRASH. THE TRANSFER CASE INTERCOOLER LOOP IS INSIDE THE TRANSFER CASE OF THE HUMMER. TRANSMISSION FLUID FROM THE 4L80E AUTOMATIC TRANSMISSION CIRCULATES THROUGH THIS ALUMINUM FINNED COOLING LOOP AND TRANSFERS HEAT TO AND FROM THE TRANSFER CASE FLUID, WHICH IS PHYSICALLY ISOLATED FROM THE TRANSMISSION FLUID BY THE INTERCOOLER LOOP, TO THE TRANSMISSION FLUID, WHICH IS THEN CIRCULATED THROUGH THE TRANSMISSION OIL COOLER AT THE FRONT OF THE VEHICLE AND RETURNED TO THE TRANSMISSION. DUE TO IMPROPER DESIGN, THE INTERCOOLER LOOP MOVES AND VIBRATES INSIDE THE TRANSFER CASE AND OVER TIME DEVELOPS STRESS FRACTURES NEAR THE INPUT NIPPLE. THIS CAUSES ATF TO BE PUMPED FROM THE TRANSMISSION INTO THE TRANSFER CASE, AND FROM THERE INTO THE HUMMER VENT SYSTEM WHICH CONNECTS THE GEARED HUBS, DIFFERENTIALS AND AIR CLEANER. THERE IS USUALLY NO EXTERNAL INDICATION OF FLUID LOSS, AND EVENTUALLY, DEPENDING ON THE SEVERITY OF THE CRACKS, LOW ATF LEVELS CAUSE THE TRANSMISSION TO BE DESTROYED, POSSIBLY CATASTROPHICALLY, AND POSSIBLY AT HIGH SPEEDS, WHICH MAY POSE A SEVERE SAFETY HAZARD. IN MY CASE, I NOTICED A CLOUD OF WHITE SMOKE BEHIND MY VEHICLE AS I DROVE AT 75 MPH DOWN I-25 OUTSIDE DENVER. I WAS ABLE TO STOP BEFORE THE TRANSMISSION SEIZED, BUT THE ONLY REASON I NOTICED THE PROBLEM WAS BECAUSE A PLASTIC VENT LINE SOFTENED AND RUPTURED, SPILLING ATF ONTO THE EXHAUST PIPE...WHICH CREATED A SIGNIFICANT FIRE HAZARD. MY TRANSMISSION WAS DAMAGED AND HAD TO BE REPLACED AS A RESULT, AND THE CAUSE OF THE FAILURE WAS TRACED TO THE DEFECTIVE INTERCOOLER LOOP IN THE TRANSFER CASE. THIS INTERCOOLER LOOP FAILURE HAS BEEN EX
- NHTSA ID
- 700469
- Incident
- Oct 1, 1996